Metric hex keys, are often called Allen(R) keys (named after the inventor, Allen Manufacturing Company of Hartford, Connecticut). They are made of alloy steel and come short and long arm. (Ball end and t-handle are available upon request). The tool is usually held and twisted by its long side, creating torque at the tip of the short side; it can also be held by its short arm to access screws in difficult-to-reach locations and to turn screws faster at the expense of torque. Sets are also available in both metric and standard sizes.